The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to us of any royalties thereon.
Incorporation of two or more spectral bands in a missile seeker is not a new idea and is desired for various reasons, among others, such as improving target acquisition and aimpoint selections, hardening the seeker against potential countermeasures, enhancing the capability to attack low-signature targets and air defense suppression capabilities. The introduction of multi-spectrum seekers into field weapon systems, however, has been limited due, at least in part, to the significant increase in the cost and size of a seeker having two or more sensors in different regions of the electromagnetic spectrum and lack of maturity in component technology to allow the separation of spectral bands while minimizing losses.
Since the conception of the photonic band gap (PBG) crystal in 1987, there has been a steady growth in the published literature on the subject. PBG crystals, which can be easily fabricated in one, two or three dimensions in the millimeter and microwave regions of the electromagnetic spectrum, are periodic dielectric lattices that exhibit frequency stop bands over which electro-magnetic wave propagation cannot occur.
The photonic band gap (PBG) dual-spectrum sensor utilizes the frequency-selective properties of a photonic band gap device constructed in accordance with this invention to separate electromagnetic wave entering through a common aperture into two frequency bands. The parameters of the PBG device are chosen so that one frequency band is transmitted through the device with low attenuation while the second band is reflected with low attenuation from the front face of the device. This separation of the two bands allows separate detection processes to be performed to recover the information content of the two signals before the information is fused in subsequent signal processing operation. Further, the fact that the PBG crystal bandgap can be tailored by the proper selection of material properties gives the sensor designer a wider range of choices than are available from conventional materials.